Control of water quality in both freshwater and marine aquariums is usually conducted by means of filtration systems. These filtration systems comprise mechanical filtration means for organic material and means for the biological conversion of ammonia to nitrate by immobilized nitrifying bacteria. Nitrate, the end product of nitrification, accumulates in the water and is usually not removed.
With the booming interest in the aquarium hobby and, consequently, the introduction of new exotic ornamental fish species, higher demands are set with regard to the water quality in aquariums. Much of the recent literature in this field stresses the need for nitrate removal for several reasons:
1. some ornamental fish species are unable to propagate or grow in water containing high nitrate levels (e.g. softwater fish species such as discus, marine fish species). PA1 2. high nitrate levels in aquariums stimulate undesired algal growth on the walls of the aquaria (fouling). PA1 1) the absence of oxygen, PA1 2) the presence of a degradable organic carbon source to serve as feed for denitrifiers.
Until a few years ago no systems for nitrate removal from aquariums were commercially available and nitrate concentrations were controlled by periodical dilution of the aquarium water with clean water. Today, only a limited number of commercial biofiltration systems tuned at nitrate removal from aquariums are available.
These filters are based on the principle of creating conditions which stimulate growth of denitrifying bacteria that reduce nitrate to nitrogen gas. Conditions for the growth of these denitrifying bacteria are:
Unlike filters used for ammonia removal, the performance of denitrifying filters is often erratic and their successful use largely depends on the skills and experience of the operator. Specifically, it is often difficult to pass water to be treated through an anoxic, denitrifying zone without causing oxygen enrichment of this zone. Furthermore, addition of a carbon source is most difficult to balance: Too much carbon addition will cause a wash-out and pollution of the aquarium water whereas too little carbon will lead to incomplete denitrification and often to accumulation of toxic nitrite.
Considering the existing need for nitrate removal from aquariums and, furthermore, problems encountered with the few commercially-available filters for nitrate removal, it can be concluded that a need exists for denitrifying filters that are easy to operate and bring about a rapid removal of nitrate from aquariums.
The novel polymeric beads of the present invention can also be used for the removal of excess nitrate content form various effluents and from any aqueous medium having too high a nitrate content.